I have same issue. Sometimes imei seems as same as on backside print of the phone and sometimes disappears. I tried everything. I went to AppStore also and they said they have nothing to do. They said it seems my phone hacked or my motherboard has been changed! Altough i have never seen.
Yes i droped a few times my phone but is was still working. It was on "searching" not just after the drop.
Without a reason it is stucking on searching position...